Thread: Wing Extensions
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Old July 22nd 03, 02:45 AM
Peter Dohm
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Jay wrote:

I think the poster meant that for that particular case the numbers
didn't change much. But in general, there aren't many parts of the
plane that effect performance more than the wing does. Produces
effectively all the lift and most of the drag.


I really had planned to stay out of this; but ...

The wing certainly produces most of the lift on a typical (not Rutan)
airplane, although the fuselage, in many common designs, contributes
significant lift as well; especially at low speed and high angle of
attack.

However, the wing does not contribute most of the drag. Typical wings
have L/D of around 100/1 for laminar and ... aarrrgh! ... I can't
find my Dover Edition of "Theory of Wing Sections", but even the
"rough" condition gives more than 30/1 for cruise and is still good
enough to contribute less than half of the total drag at climb speed.

The fuselage and engine cooling are usually the biggest contributors;
with enpenage, undercarriage, antennas, and other "stuff" that sticks
out of the airplane contributing lesser amounts of drag.

Therefore, the probable contribution of wing extensions on most powered
aircraft should be reduced climb and approach speeds and the opportunity
to reduce fuel consumption in a reduced speed cruise. Assuming that the
aircraft was correctly rigged for its cruising speed; then it should be
than the shorter winged slower at its cruising speed version due to the
nose down attitude of the fuselage as well as the related increased trim
drag of the empenage. The increased drag of the larger wing should make
a lesser contribution to the greater drag.

Peter


Dave Hyde wrote in message ...
Roger Halstead wrote:

I guess you'd need some sort of plastic overlay for the airspeed
indicator to remind you of the new critial speeds.

They don't change all that much. You leave them set for the shorter
wing. ...


I think someone else said this too, and I find it confusing. If they
don't change that much, why have the extensions? Just for more fuel?

The airpseed indicator could certainly be marked that way
and inspectors may approve it, but it seems like the long-wing version
would be more critical for safety numbers. Vne would likely be lower
for the long wing(*), and maneuvering speed will be lower as well,
assuming the extensions add any lift at all. Stall speed for *both*
wings is important.

(*) Assuming it's flutter that sets Vne, which is a
big assumption.

Dave 'corner speed' Hyde

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